It is well known to control the air/fuel ratio of an engine having two cylinder banks in response to an exhaust gas oxygen sensor coupled to each of the banks. U.S. Pat. No. 5,074,113 discloses such an air/fuel control system wherein the exhaust manifold of each engine bank is coupled to a single catalytic converter via y-pipe.
The inventors herein have recognized a problem with the above approaches having a single catalytic converter coupled to each engine bank. When one back runs lean of stoichiometry, while the other bank runs rich of stoichiometry, less than 100% converter efficiency is achieved.